Systems and methods for improving cell balancing and cell failure detection

ABSTRACT

In one aspect, an embodiment of this invention comprises an energy storage device balancing apparatus. The energy storage device balancing apparatus comprises a balancing circuit and an alarm circuit. Both the balancing circuit and the alarm circuit are coupled to the energy storage device. The balancing circuit is configured to monitor a voltage of the energy storage cell and dissipate energy from the energy storage cell if the voltage is at or above a first reference voltage. The alarm circuit is configured to generate an alarm when the voltage of the energy storage cell is at or above a second reference voltage and dissipate energy from the energy storage cell when the voltage is at or above the second reference voltage.

BACKGROUND

Field

The present disclosure relates generally to energy storage devices andsystems, such as batteries and capacitors modules and systems, includingultracapacitors and super-capacitors, and in particular, capacitors orbatteries deployed in modules, each module containing some number ofbattery and/or capacitor cells.

Description of the Related Art

Various systems and techniques exist for balancing the voltage ofindividual cells in an energy storage system by discharging an excesscell voltage. However, prior approaches do not fully and efficientlydissipate excess cell voltage and require expensive components.

Additionally, systems and techniques for balancing modules may not becapable of discharging negative voltages in one or more of theindividual cells that form the modules being balanced. These negativevoltages may present problems in such systems.

Additionally, systems and techniques exist for detecting failure in anenergy storage system and issuing an alarm, but they often fail due toexcess voltages from the energy storage system. In some systems andtechniques, separate but redundant alarm systems may be used to monitorand alert for various module-wide conditions. For example, an open cellcondition in a module (e.g., where an entire voltage of the module, upto 750 volts (V) in this case) may be expressed on the alarm circuit ofthe module and may destroy the alarm circuit. Thus, a redundant circuit,capable of surviving a high voltage (e.g., 750V) is needed to provide asustained alarm in varied conditions.

SUMMARY

Embodiments disclosed herein address the above-mentioned problems withprior art. The systems, methods and devices of this disclosure each haveseveral innovative aspects, no single one of which is solely responsiblefor the desirable attributes disclosed herein.

Various embodiments of methods and devices within the scope of theappended claims each have several aspects, no single one of which issolely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

In one aspect, an embodiment of this invention comprises an energystorage device balancing apparatus. The energy storage device balancingapparatus comprises a balancing circuit and an alarm circuit. Both thebalancing circuit and the alarm circuit are coupled to the energystorage device. The balancing circuit is configured to monitor a voltageof the energy storage cell and dissipate energy from the energy storagecell if the voltage is at or above a first reference voltage. The alarmcircuit is configured to generate an alarm when the voltage of theenergy storage cell is at or above a second reference voltage anddissipate energy from the energy storage cell when the voltage is at orabove the second reference voltage.

Additionally, in some embodiments of the aspect, the balancing circuitdissipates energy from the energy storage cell by conducting adischarging current through at least one of a passive dissipativecomponent and an active dissipative component. In some embodiments, thealarm circuit dissipates energy from the energy storage cell byconducting a discharging current through at least one of a passivedissipative component and an active dissipative component.

In some aspects, the alarm circuit dissipates energy from the energystorage cell by conducting a discharging current through a resistor. Insome aspects, the balancing circuit comprises a shunt regulatorconfigured to operate in a comparator mode.

In another aspect, an embodiment of the invention comprises an energystorage device cell balancing apparatus. The energy storage device cellbalancing apparatus comprises a first dissipative component and a seconddissipative component, both coupled to an energy storage cell. The firstdissipative component is configured to monitor a voltage of the energystorage cell dissipate energy from the energy storage cell if thevoltage is at or above a positive threshold voltage by conducting adischarging current through the first dissipative component. The seconddissipative component is configured to dissipate a negative voltage fromthe energy storage cell.

In some aspects, the second dissipative component is coupled in seriesto a diode, the diode configured to provide a path for discharge of thenegative voltage of the energy storage cell through the seconddissipative component. In some other aspects, the second dissipativecomponent is further configured to dissipate positive energy from theenergy storage cell if the voltage is at or above the positive thresholdvoltage by a discharging current through the second dissipativecomponent when the cell is positively charged. In some embodiments, thefirst dissipative component is further configured to dissipate energyfrom the energy storage cell if the voltage is at or above the positivereference voltage by conducting a discharging current through the firstdissipative component.

In some aspects, the second dissipative component comprises at least oneof a passive dissipative component and an active dissipative component.In some other aspects, the second dissipative component comprises aresistor.

In an additional aspect, an embodiment of the invention comprises anovervoltage alarm conveying apparatus. The overvoltage alarm conveyingapparatus comprises an overvoltage alarm circuit, a Zener diode, anisolating device, and a current limiting circuit. The overvoltage alarmcircuit is configured to generate an overvoltage alarm signal based on areceived overvoltage signal. The isolating device is configured toprovide an isolated output signal. The current limiting circuit isconfigured to provide a current flow through the Zener diode to theisolating device when exposed to a voltage exceeding a rating of theZener diode. The Zener diode, the isolating device, and the currentlimiting circuit are configured to maintain the overvoltage alarm signalgenerated by the overvoltage alarm circuit if the overvoltage alarmcircuit is unable to maintain the overvoltage alarm signal itself.

BRIEF DESCRIPTION OF THE DRAWINGS

Details of one or more embodiments of the subject matter described inthis disclosure are set forth in the accompanying drawings and thedescription below. Although the examples provided in this disclosure aresometimes described in terms of capacitors or capacitor cells, theconcepts provided herein may apply to other types of energy storagesystems. Other features, aspects, and advantages will become apparentfrom the description, the drawings and the claims. Note that therelative dimensions of the following figures may not be drawn to scale.

FIG. 1 illustrates an embodiment of a balance and overvoltage alarmcircuit comprising a balancing circuit in which an integrated alarmcircuit discharges voltage when the balance and overvoltage alarmcircuit is exposed to a cell or module experiencing an overvoltagecondition.

FIG. 2 illustrates an embodiment of a balancing circuit in which adissipative component discharges a negatively charged cell to which thebalancing circuit is coupled when the dissipative component is coupledin series to a diode.

FIG. 3 illustrates another embodiment of a balancing circuit in which adissipative component discharges the negatively charged cell to whichthe balancing circuit is coupled when the dissipative component iscoupled in series to a diode that is parallel to a controlled switch.

FIG. 4 illustrates an embodiment of an alarm system 400 comprising aredundant cell overvoltage alarm circuit 402 for communication ofovervoltage conditions to an external alarm monitoring circuit.

FIG. 5 illustrates an embodiment of an alarm system comprising acombined cell and module overvoltage alarm circuit for communication ofovervoltage conditions to the external alarm monitoring circuit.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments and isnot intended to represent the only embodiments in which the inventionmay be practiced. The term “exemplary” used throughout this descriptionmeans “serving as an example, instance, or illustration,” and should notnecessarily be construed as preferred or advantageous over otherexemplary embodiments. The detailed description includes specifieddetails for the purpose of providing a thorough understanding of theexemplary embodiments. In some instances, some devices are shown inblock diagram form.

Energy storage systems can include a plurality of individual battery orultracapacitor cells arranged in series to form an energy storage moduleor bank which has a higher voltage output than an individual cell. Themodules in turn can be connected in series with other modules to outputhigher combined voltages. The individual capacitors or batteries of amodule are sometimes referred to as capacitor cells or battery cells,respectively, or more generally, cells.

Excessive cell voltage can damage an individual cell, the module inwhich the cell is located, or both. Cell balancing circuits (“balancingcircuits”) can be used to discharge battery or ultracapacitor cells toequalize cell voltages and prevent or minimize damage caused byexcessive cell voltage conditions. Such excessive cell voltage can bedischarged by one or more of a passive component, for example one ormore resistors, and an active component, for example one or moretransistors or regulators, in the balancing circuit.

A passive dissipative component may be unable to individually control aflow of current, while an active dissipative component may be capable ofcontrolling current flow. Both active and passive dissipative componentsmay dissipate voltage. In some embodiments, the passive dissipativecomponents may discharge voltage through constant current discharge orthrough resistive discharge. In the case of a constant current dischargecircuit, a constant discharge current is drawn from the cell,independent of the cell voltage or the voltage being discharged. Aresistive discharge circuit draws a discharge current that isproportional to the cell voltage. As the voltage of the cell increases,the discharge current also increases and vice versa. Examples of passivedissipative components may include fixed resistors, variable resistors,thermistors, passive attenuators, potentiometers, etc. Examples ofactive dissipative components may include transistors, regulators,active attenuators, active diodes, etc.

Some of the embodiments of the balancing circuits described herein allowfor splitting the actual voltage dissipation between both the active andpassive components. This may increase the efficiency of the voltagedissipation, may reduce the number of components needed, and mayeliminate the need for some expensive active or passive components,relative to previous cell balancing circuits.

Improved Cell Balancing Circuit

In some embodiments, the cell balancing circuits described herein arecoupled to one or more alarm circuits. These alarm circuits may providean indication of an overvoltage condition to a user or to an externalcircuit. For example, the alarm circuits may be coupled to an indicatorlight or an audible alarm.

In some embodiments, the cell balancing circuits comprising the activeand passive dissipative components may be limited in their overvoltagedischarge rates. Balanced cells increase available energy from themodule. Accordingly, faster balancing allows faster arrival at a maximumenergy state for the module. In some embodiments, additional activeand/or passive dissipative components may be added to the balancingcircuits, thus increasing the cost and complexity of the balancingcircuits. Alternatively, or additionally, in some embodiments, theovervoltage alarm circuit may provide voltage dissipation in conjunctionwith the voltage dissipation properties of the active and/or passivedissipative components of the balancing circuit. By combining the alarmfunctions with the balancing functions, total cost for the balancingcircuits and alarm circuits can be reduced.

FIG. 1 illustrates an embodiment of a balance and overvoltage alarmcircuit 100 comprising a balancing circuit 140 a and an integratedbalancing and alarm circuit 130. The balancing circuit 140 a maydischarge voltage when coupled to a cell or module experiencing anovervoltage condition. The balancing and alarm circuit 130 may alsodischarge voltage when coupled to the cell or module the overvoltagecondition that triggers the alarm. The balance and overvoltage alarmcircuit 100 may be coupled to or may include an energy storage cell. Forexample, the balance and overvoltage alarm circuit 100 may be externalto and connected in parallel to the energy storage cell, for example atnodes 124 and 126. The energy storage cell can include single ormultiple batteries, capacitors, ultracapacitors or other alternativemeans of energy storage, or can be combined with a plurality of similarcells, each with a corresponding balance and overvoltage alarm circuit,to form an energy storage module. Thus, in some embodiments, a pluralityof balance and overvoltage alarm circuits 100 can be implemented for useon a module, with each overvoltage alarm circuit providing functionalityto a corresponding cell within the module. For ease of descriptionherein, the energy storage cell may include either the single cell orthe module either internal or external to the balance and overvoltagealarm circuit 100.

The balancing circuit 140 a of the balance and overvoltage alarm circuit100 can include one or more shared-dissipation balancing circuits,illustrated here as shared-dissipation balancing circuit 140 a. More orfewer shared-dissipation balancing circuits 140 a may be included in thebalance and overvoltage alarm circuit 100 than shown in FIG. 1. In someembodiments, other circuit variations of dissipating balancing circuits140 may be included in the balance and overvoltage alarm circuit 100.The shared-dissipation balancing circuit 140 a shown in FIG. 1 mayinclude a resistive divider, an active dissipative component, and apassive dissipative component. For the shared-dissipation balancingcircuit 140 a, the resistive divider may comprise resistors 102 and 104;the active dissipative component may comprise a shunt regulator 108; thepassive dissipative component may comprise a resistor 106.

The resistive divider comprising resistors 102 and 104 may allow theactive dissipative component 108 to conduct a discharging current at avoltage value different than a built-in reference value of the activedissipative component 108. For example, the resistors 102 and 104 mayoffset an initial voltage from which the active dissipative component108 begins conducting a discharge current. Thus, the resistive dividerformed from the resistors 102 and 104 may allow the active dissipativecomponent 108 to be more versatile and enable usage in more voltageranges.

The active dissipative component 108 can comprise a three-terminaldevice, having terminals 1, 2, and 3. The terminal 1 can be a referenceterminal connected to a node 128 between the resistors 102 and 104 ofthe dissipating balancing circuit 140 a. Thus, the active component 108may monitor a voltage of the resistor divider at the node 128. If thevoltage of the resistive divider at the node 128 rises above a thresholdvoltage, for example 2.5 volts (V), the active dissipative component 108can allow a discharging current to flow from the energy storage cellthrough the active component terminals 2 and 3 and the passivedissipative component 106, thus causing the excess cell voltage of theenergy storage cell to dissipate across both the active and passivecomponents 108 and 106, respectively.

In some embodiments, a shunt regulator, for example a Texas Instruments®TL431 shunt regulator, can be used to implement the active dissipativecomponent 108. The active component 108 may monitor the voltage of theenergy storage cell by configuring the shunt regulator in a comparatormode with a preset or built-in reference voltage, for example 2.5V. Insome embodiments, the preset or built-in reference voltage may be usersettable. The active dissipative component 108 can further include anoutput transistor (not shown). When the voltage of the energy storagecell exceeds the reference voltage, the comparator may activate or turnon the output transistor in an unsaturation mode, thereby causing adischarging current to flow through both the passive component 106 andthe active component 108 and causing both the passive component 106 andthe active component 108 to dissipate excess cell voltage. In someembodiments, the output transistor of the active component 108 maymaintain a maximum constant voltage drop across the active component108. For example, in some embodiments this maximum constant voltage dropcan be approximately 2 V. Any additional excess cell voltage of theenergy storage cell is dropped (or dissipated) across the passivecomponent 106. In some embodiments, the passive component 106 maycomprise any device or set of devices configured to passively dissipatevoltage. In some embodiments, the active component 108 may comprise anydevices or set of devices configured to monitor a voltage and activelydissipate voltage. In some embodiments, the active component 108 maycomprise separate devices that measure the voltage and control activevoltage dissipation and flow. Accordingly, dissipation in the balancingcircuit 140 a may be shared between both the passive and activedissipative components 106 and 108, respectively.

The balancing circuit of the integrated balancing and alarm circuit 130can function similarly to balancing circuit 140 a. The shareddissipation of the balancing circuit of the integrated balancing andalarm circuit 130 may allow for more efficient voltage dissipation, aswell as fewer parts, and lower cost components, and thus lower overallcost as compared to the dissipating balancing circuit 140 a, among otherbenefits, than balancing circuits with solely active or solely passivecomponents. In some embodiments, such benefits can be recognized, evenwhen two or more shared-dissipation circuits are implemented, whileimproving additional functional improvements, such as speed ofdissipation.

The balancing circuit of the balancing and alarm circuit 130 maycomprise resistors 110 and 112; the active dissipative component maycomprise a shunt regulator 114; the passive dissipative component maycomprise a resistor 116. The overvoltage alarm circuit 132 of thebalancing and alarm circuit 130 may comprise a resistor 118, atransistor 120, and a diode 122. In some embodiments, the overvoltagealarm circuit 132 may feed a summing circuit or similar circuit, wherethe overvoltage alarm circuits from a plurality of cells or modules aremonitored together. The transistor 120 may act as a switch controlled bythe shunt regulator 114 of the balancing and alarm circuit 130. Theresistor 118 may be shunted by an emitter-base junction of transistor120. In some embodiments, the shut regulator 114 may be replaced with anintegrated circuit configured to perform similar functions.

In some embodiments, one or both of the balancing circuit 140 a and thebalancing circuit of the balancing and alarm circuit 130 may be replacedby alternative balancing circuits.

An alternative balancing circuit may include an active component havingtwo terminals for voltage inputs and an output terminal. The activecomponent of this alternative balancing circuit can monitor the voltageof the coupled cell via the voltage input terminals and output a signalat its output terminal if the voltage of the coupled cell rises above apredetermined threshold voltage. The other alternative balancing circuitcan additionally include resistors and a transistor. The output signalfrom the active component can be provided, via a first of the resistors,to the transistor. The transistor can act as a switch controlled by thesignal output, where the signal output activates or turns on thetransistor. When the transistor activates, it creates a path from thecoupled cell through a second resistor and the transistor, therebyproviding a resistive discharge (variable current) that may dissipatethe excess voltage of the coupled cell. This other alternative balancingcircuit may mainly dissipate the excess cell voltage through the secondresistor. The first resistor and transistor may not contributesignificantly to discharging the excess cell voltage.

A second alternative balancing circuit can also be coupled to the celland may include an active component and a passive component. The activecomponent can be a three-terminal device. One of the terminals can be areference terminal by which the active component may monitor the voltageof the coupled cell. If the voltage of the coupled cell rises above athreshold voltage, the active component can allow a discharging currentto flow from the coupled cell through the active component and thepassive component, thus causing the excess cell voltage to dissipateacross both the active and passive components. In some embodiments, asdescribed herein, a shunt regulator, for example a Texas Instruments®TL431 shunt regulator, can be used to implement the active component.

A third balancing circuit may be similar in structure to the second,shared-dissipation balancing circuit. The third balancing circuit may bea linear embodiment of the second balancing circuit. Accordingly, thereference terminal of the active component of the third balancingcircuit may couple to a node between the active component and thepassive component. Thus, the active component can be configured tomonitor the voltage at this node.

The balance and overvoltage alarm circuit 100 may discharge anovervoltage cell or module faster than a balancing circuit alone. Insome embodiments, the balance and overvoltage alarm circuit 100 mayprovide a multi-stage balancing method. For example, the balancingcircuit 140 a of the balance and overvoltage alarm circuit 100 mayprovide a first stage of balancing while the balancing and alarm circuit130 may provide a second stage of balancing. Accordingly, the balancingand alarm circuit 130 may dissipate voltage only when the voltage of thecoupled cell exceeds a second specified threshold, while the balancingcircuit 140 a may dissipate voltage when the voltage of the coupled cellexceeds a first specified threshold that is different than and lowerthan the second specified threshold. For example, there may be threestates of voltage dissipation: (1) a state where neither the balancingcircuit 140 a nor the balancing and alarm circuit 130 dissipate voltage(voltage of the cell is less than both the first and second specifiedthresholds); (2) a state where only the balancing circuit 140 a isdissipating voltage (voltage of the cell is greater than the firstspecified threshold but less than the second specified threshold); and(3) a state where both the balancing circuit 140 a and the balancing andalarm circuit 130 both dissipate voltage (voltage of the cell is greaterthan both the first and second specified thresholds).

In some embodiments, the balance and overvoltage alarm circuit 100 maybe integrated into cell management systems or in other systems where thecell or module balance voltage or level is below an overvoltage alarmvoltage or level. Accordingly, in some embodiments, the balancing andalarm circuit 130 may only be used as a dissipative component when thecell or module overvoltage exceeds a specified threshold, for example anovervoltage that activates the overvoltage alarm. The specifiedthreshold may be equal to or greater than, but not less than thethreshold at which the balancing circuit 140 a acts to dissipate voltagefrom an overvoltage cell or module. Thus, the balance and overvoltagealarm circuit 100 may be configured to utilize one or both of thebalancing circuit 140 a and the balancing and alarm circuit 130 todissipate the overvoltage cell or module in any given instance, whilethe overvoltage alarm circuit 132 indicates the overvoltage alarmcondition while the balancing circuit of the balancing and alarm circuit130 dissipates voltage.

Embodiments of the circuit(s) described herein may improve efficiency ofthe excess voltage discharge compared to other circuits, where thebenefits of one or both of the constant current discharge and theproportional discharge can be maintained and implemented as both theactive and passive components participate in the excess voltagedischarge. Additionally, the improved circuits may allow for morediverse applications where the circuit may require fewer, less expensive(and smaller) components and thus may require less space to beimplemented. The balancing and alarm circuit 130 may provide additionalcell discharge current and thus increase balance current when there isan active overvoltage alarm. The balancing and alarm circuit 130 maydraw additional balance current to accelerate discharge of the coupledcell with a charge above the overvoltage limit, thus providing forequalization of cell voltages more quickly than the balancing circuit140 a operating alone but without adding additional components to theoverall system. The combined balance and overvoltage alarm circuit maybe applied to cell management systems where the balance level is lessthan an overvoltage alarm level where cell balancing using the balancingcircuit 140 a begins before cell balancing using the balancing and alarmcircuit 130.

Negative Charge Dissipation Circuit

In some embodiments, the cell balancing circuits described herein arecoupled to one or more modules comprising a plurality of cells. Whendissipating voltage from these modules, for example from a high currentdown to a low voltage (e.g., zero volts), it is possible that one ormore of the plurality of cells may result in a negative (or reverse)voltage while the overall module measures the low voltage (e.g., zerovolts). For example, although the module measures approximately zerovolts, it is possible that one cell forming the module has a voltage of+1V while another cell forming the module has a voltage of −1V. Anegatively charged cell may be dangerous in a module comprising aplurality of cells. In some embodiments, a negatively charged cell mayreduce an overall voltage of the module comprising the negativelycharged cell. In some embodiments, a negative voltage in a cell mayshorten the life of the cell. However, the balancing circuit for thecells forming the module may include components that are capable ofdischarging the negative voltage.

FIG. 2 illustrates an embodiment of a balancing circuit 200 comprising adissipative component 206 which discharges a negatively charged cell towhich the balancing circuit 200 is coupled. The dissipative component206 can be coupled in series to a diode 208, which also dissipates atleast a portion of the voltage of the negatively charged cell to whichthe diode 208 is coupled. The balancing circuit 200 may be coupled to ormay include an energy storage cell. For example, the balancing circuit200 may be external to and connected in parallel to the energy storagecell, for example at nodes 210 and 212. The energy storage cell caninclude single or multiple batteries, capacitors, ultracapacitors orother alternative means of energy storage, or can be combined with aplurality of similar cells, each with a corresponding balance andovervoltage alarm circuit, to form an energy storage module. For ease ofdescription herein, the energy storage cell may include either thesingle cell or the module either internal or external to the balancingcircuit 200. For example, the single cell may comprise an ultracapacitorcell 202.

The balancing circuit 200 can further include an additional dissipativecomponent, such as an active component 204. The active component 204 canhave two terminals (terminals 2 and 3) for voltage inputs, and an outputterminal 1. In some embodiments, the active component 204 may beconfigured to monitor and dissipate positive voltage from the cell 202if the monitored positive voltage exceeds a first threshold. Forexample, the threshold voltage may be 1.5 V, and once the voltage of thecell 202 rises above 1.5 V, the active component 204 may dissipate anypositive voltage above the 1.5V threshold. However, as discussed above,the active component 204 may be unable to detect and/or dissipate anegative voltage in the cell 202.

The dissipative component 206 may be coupled to the node 210 and thediode 208. The dissipative component 206 may comprise a passivedissipative component, for example a resistor as shown. However, thedissipative component may comprise any active or passive dissipativecomponent based on specifics of the applied system, including desiredcosts, desired functionality, etc.

The balancing circuit 200 also includes the diode 208. The diode 208 maybe coupled between the node 212 and the dissipative component 206. Insome embodiments, the diode 208 may allow current flow in one directionwhen a voltage difference across the diode 208 exceeds a specifiedthreshold as defined by the diode (e.g., 0.6-0.7V difference between ananode and a cathode of the diode). As soon as cell voltage is morenegative than 0.6-0.7V, the diode 208 may become forward biased and maystart conducting and dissipating negative charge on the dissipativecomponent 206 and the diode 208 itself. The diode voltage drop mayremain at 0.7V. As shown, the diode 208 allows current flow from thenode 212 through the diode 208 and through the dissipative component 206to the node 210 when the ultracapacitor cell 202 is negatively charged.

In some embodiments, the diode 208 may be integrated with the activecomponent 204 as part of an integrated circuit (not shown) to protectthe integrated circuit. In such embodiments, the diode 208 may beconsidered an “anti-parallel diode”. Additionally, the integratedcircuit may include both the diode 208 (e.g., the antiparallel diode)and also the dissipative component 206 (not shown). For example, theactive component 204 of the integrated circuit may be configured todissipate positive voltage (as described herein) while allowing fordischarge of negative voltage through the anti-parallel diode and theintegrated dissipative component.

In some embodiments, a shunt regulator, for example a Texas Instruments®TL431 shunt regulator, can be used to implement the active component204. The active component 204 may comprise any comparator or integratedcircuit designed to detect positive voltage differences. In someembodiments, the active component 204 may comprise any devices or set ofdevices configured to monitor a positive voltage and actively dissipatethe positive voltage. In some embodiments, the active component 204 maycomprise separate devices that measure the positive voltage and controlactive positive voltage dissipation and flow. In some embodiments,positive voltage dissipation in the balancing circuit 200 may be sharedbetween both passive and active dissipative components. For example,both the active component 204 and the dissipative component 206 maydissipate positive voltage, where the dissipative component 206 is apassive component (e.g., the resistor).

FIG. 3 illustrates an embodiment of a balancing circuit 250. Thebalancing circuit 250 may be coupled to or may include the energystorage cell 202. The balancing circuit 250 can include the activecomponent 204, the dissipative component 206, and the diode 208, similarto those components described above in relation to the balancing circuit200 and the cell 202, which will not be described again for purposes ofbrevity.

In this embodiment, the output signal of the active component 204 maycontrol a transistor 220, which in turn may control current flow throughthe dissipative component 206 for positive voltage dissipation. Thecurrent flow through the transistor 220 and the dissipative component206 may be opposite in direction to current flow through the diode 208and the dissipative component 206 for negative voltage dissipation. Thetransistor 220 may be coupled to the node 210 and the dissipativecomponent 206 in parallel to the diode 208. The transistor 220 mayprovide a current path through the dissipative component 206 when theultracapacitor cell 202 is positively charged, not shown here.

The balancing circuits 200 and 250 as described in relation to FIGS. 2and 3 may utilize the dissipative component 206 (e.g., the resistor) todischarge the negatively charged cell (e.g., the ultracapacitor 202)coupled to the balancing circuits 200 and 250 via the diode 208. In someembodiments, the diode 208 may be an integrated in an integrated circuitwith one or more of the active component 204 and the transistor 220 asthe anti-parallel diode. Regardless of the configuration of thebalancing circuits 200 and 250, the balancing circuits 200 and 250 arecapable of discharging negatively charged modules or cells quickly andsafely via the diode 208 and the dissipative component 206 (which may beactive or passive).

Combined Cell, Module, and Redundant Overvoltage Alarm Circuit

As described herein, modules or cells may comprise overvoltage alarmcircuits. In some applications, individual-cell overvoltage detector oralarm circuits or module overvoltage detector or alarm circuits generatethe alarm. The cell and module alarm circuits may provide an indicationof an overvoltage condition to a user or to an external circuit. Forexample, the alarm circuits may be coupled to an indicator light or anaudible alarm. Additional alarm monitoring circuits can monitor or lookfor these alarms periodically. When a system comprises both cell andmodule overvoltage alarm circuits, alarms generated by the modulecircuits and alarms generated by the cell circuits may be individuallycommunicated to the alarm monitoring circuits, for example usingindividual optocouplers.

One of the most catastrophic failures in serially connected modules isan open cell failure. In such a failure, the entire voltage of thestring of cells (e.g., in this specific case 750V) may be expressedacross the alarm monitoring circuit of one cell or one module. This highvoltage may destroy or otherwise incapacitate the existing overvoltagealarm circuit and may stop the overvoltage alarm being generated.

A redundant or open cell overvoltage alarm circuit may survive such anevent and continue to send the overvoltage alarm to the user or theexternal circuit even if the rest of the circuit (e.g., the alarmmonitoring circuit) is destroyed. This redundant circuit cannot be resetas long as high voltage is present, and thus will maintain theovervoltage alarm as long as the overvoltage condition exists. In someembodiments, the overvoltage alarm monitoring circuits and the redundantcircuits may be integrated into a simpler combined circuit, whichresults in fewer components between the two circuits.

FIG. 4 illustrates an embodiment of an alarm system 400 comprising acell overvoltage alarm circuit 402 for communication of overvoltageconditions to an external alarm monitoring circuit. The alarm system 400includes the cell overvoltage alarm circuit 402, the ultracapacitormodule 410, a transistor 412, a first optocoupler 414 and resistor 420.A second, redundant overvoltage alarm system consists of the optocoupler416, a Zener diode 422, and a current limit circuit 424 in series withthe optocoupler 416. A node 406 voltage to ground is a single modulevoltage under normal conditions and a whole series string of modulesvoltage during and after an open cell failure condition. The first andsecond optocouplers 414 and 416, respectively, may be coupled to or partof the external alarm monitoring circuit. As shown in the alarm system400, when one or more of the cells of the module experience anovervoltage condition, the individual alarm circuit (e.g., the alarmcircuit 132 of FIG. 1) may activate and output an alarm signal. Thecorresponding output alarm signals from each of a plurality of cellsforming a particular module may be coupled together to create a combinedoutput of the cell overvoltage alarm circuit 402. This combined outputmay then control the transistor 412. Thus, when one of more of the cellsof the module experience the overvoltage condition, the output alarmsignal of the cell overvoltage alarm circuit 402 may turn on or activatethe transistor 412. By turning on the transistor 412, a current path iscreated from the ultracapacitor module 410 (e.g., at node 406) throughthe resistor 420, the optocoupler 414, and the transistor 412 to ground.Accordingly, when one of the cells experience the overvoltage condition,the transistor 412 closes and current passes through the optocoupler414, conveying the overvoltage condition to a secondary system (notshown).

For the redundant overvoltage alarm circuit, the Zener diode 422 iscoupled between the node 406 and the current limit circuit 424 to makesure that redundant alarm starts operating at a voltage higher thansingle module voltage. The Zener diode 422 may offset a full positivevoltage of the ultracapacitor module 410 based on a Zener voltage of theZener diode 422. In some embodiments, the Zener voltage may be set basedon the single module voltage. The current limit circuit 424 may limitcurrent through the optocoupler 416 and can survive indefinitely veryhigh voltage (e.g., 750V) in our embodiment. In some embodiments, thecurrent limit circuit limits currents to a safe level (e.g., 5 mA)regardless of the voltage applied (e.g., up to 800V).

In some embodiments, the optocouplers 414 and 416 may be isolatingsignal transfer devices between two circuits or systems (e.g., isolatingthe potentially dangerous ultracapacitor module full string voltage froma secondary instrumentation system). Alternative alarm devices can beused in lieu of the optocouplers 414 and 416. In some applications, thesecondary system can be implemented in a dashboard or display of avehicle comprising the cells and modules having the cell overvoltagealarm circuit 402, where the generated alarm can be seen by a vehicleoperator, for example via illumination of an LED or other visually,audibly, or tactilely perceivable means. In some embodiments, the alarmmay be communicable such that a remote operator or viewer may track thealarm.

As shown, the overvoltage alarm circuit 402 and the current limitcircuit 424 and corresponding alarm signals duplicate some components,most notably the optocouplers 414 and 416. Additionally, in order toactivate the overvoltage alarm output signal and activate theoptocoupler 414, the ultracapacitor module 410 (and the node 406) may beat a minimum voltage that would activate the optocoupler 414 after beingreduced by the resistor 420. In some embodiments, a value and a powerrating of the resistor 420 (or similar component) may be selected tolimit current through optocoupler 414 when the module voltage is at ahighest nominal module voltage. Accordingly, this value and/or powerrating establishes a certain minimum module voltage necessary foroperation of the optocoupler 414.

FIG. 5 illustrates an embodiment of an alarm system 500 forcommunication of overvoltage conditions to an external alarm monitoringcircuit, such as the external alarm monitoring circuit described hereinwith reference to FIG. 4. The alarm system 500 shares many of thecomponents with similar numbering scheme as the alarm system 400.Details of such shared components are described above in relation to thealarm system 400 and will not be described again for purposes ofbrevity.

As shown in the alarm system 500, when one or more of the cells of themodule experience an overvoltage condition, the individual alarm circuit(e.g., the alarm circuit 132 of FIG. 1) may activate and output an alarmsignal. The output alarm signals from a plurality of cells forming aparticular module may be coupled together to create an output of thecell overvoltage alarm circuit 502. This combined output or any cellovervoltage signal may then control the transistor 512. When one of moreof the cells of the module experience the overvoltage condition, theoutput alarm signal of the cell overvoltage alarm circuit 502 may turnon or activate the transistor 512. By turning on the transistor 512, acurrent path is created from the ultracapacitor module 510 (e.g., atnode 506) through the transistor 512 and through the optocoupler 516 toground. Accordingly, when one of the cells experiences the overvoltagecondition, the transistor 512 closes and current passes through thecurrent limit circuit 524 and the optocoupler 516, conveying theovervoltage condition to the secondary system (not shown). The currentlimit circuit 424 may limit current through the optocoupler 516 similarto as described above in relation to FIG. 4 and the alarm system 400.

The alarm system 500 eliminates the optocoupler 414 and the resistor 410while changing the transistor 412 from an NPN transistor to a PNPtransistor 512. Additionally, the transistor 512 is parallel to theZener diode 522. By reducing the number of components, costs andcomplexity of the entire alarm system 500 are reduced as compared to thealarm system 400. Additionally, by shorting Zener diode 512 in normalmode of overvoltage operation, the ultracapacitor module 510 may have areduced module voltage while generating a single cell voltageovervoltage alarm in case of single cell overvoltage in a dischargedmodule. As shown, the FIG. 5 circuit structure may require fewercomponents and reduced circuit complexity as compared to the FIG. 4circuit. Additionally, as the current limit circuit 524 may pass a lowcurrent through the optocoupler 516 and can operate at very high voltageindefinitely, the current limit circuit 524 may maintain the redundantovervoltage alarm signal through the optocoupler 516. Accordingly, acircuit board layout may allow for destruction of the regularovervoltage alarm, while the redundant alarm remains operational. Thusthe cell overvoltage alarm circuit 502 and the transistor 512 may bedestroyed but the Zener diode 522, the current limit circuit 524, andthe optocoupler 516 may continue to operate and output the overvoltagealarm signal.

The scope of the present disclosure is not intended to be limited by thespecific disclosures of preferred embodiments in this section orelsewhere in this specification, and may be defined by claims aspresented in this section or elsewhere in this specification or aspresented in the future. The language of the claims is to be interpretedbroadly based on the language employed in the claims and not limited tothe examples described in the present specification or during theprosecution of the application, which examples are to be construed asnon-exclusive.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules, circuits, and methodsteps described in connection with the embodiments disclosed herein maybe implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. The described functionalitymay be implemented in varying ways for each particular application, butsuch embodiment decisions should not be interpreted as causing adeparture from the scope of the embodiments.

The various illustrative blocks, modules, and circuits described inconnection with the embodiments disclosed herein may be implemented orperformed with a general purpose hardware processor, a Digital SignalProcessor (DSP), an Application Specified Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose hardware processor may be a microprocessor, but in thealternative, the hardware processor may be any conventional processor,controller, microcontroller, or state machine. A hardware processor mayalso be implemented as a combination of computing devices, e.g., acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

The steps of a method and functions described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a hardware processor, or in a combination ofthe two. If implemented in software, the functions may be stored on ortransmitted as one or more instructions or code on a tangible,non-transitory computer readable medium. A software module may reside inRandom Access Memory (RAM), flash memory, Read Only Memory (ROM),Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, a CDROM, or any other form of storage medium known in the art. A storagemedium is coupled to the hardware processor such that the hardwareprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the hardware processor. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer readable media. The hardware processor and the storage mediummay reside in an ASIC.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features have been described herein. It is to be understoodthat not necessarily all such advantages may be achieved in accordancewith any particular embodiment. Thus, the invention may be embodied orcarried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein.

Various modifications of the above-described embodiments will be readilyapparent, and the generic principles defined herein may be applied toother embodiments without departing from the spirit or scope of theapplication. Thus, the present application is not intended to be limitedto the embodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. An energy storage device balancing apparatuscomprising: a balancing circuit coupled to an energy storage cell andconfigured to: monitor a voltage of the energy storage cell; anddissipate a first energy from the energy storage cell if the voltage isat or above a first reference voltage; and an alarm circuit coupled tothe energy storage cell and configured to: generate an alarm when thevoltage of the energy storage cell is at or above a second referencevoltage, wherein the second reference voltage is greater than the firstreference voltage, and dissipate a second energy from the energy storagecell when the voltage is at or above the second reference voltage. 2.The apparatus of claim 1, wherein the balancing circuit dissipates thefirst energy from the energy storage cell by conducting a dischargingcurrent through at least one of a passive dissipative component and anactive dissipative component.
 3. The apparatus of claim 1, wherein thealarm circuit dissipates the second energy from the energy storage cellby conducting a discharging current through at least one of a passivedissipative component and an active dissipative component.
 4. Theapparatus of claim 1, wherein the alarm circuit dissipates the secondenergy from the energy storage cell by conducting a discharging currentthrough a resistor.
 5. The apparatus of claim 1, wherein the balancingcircuit comprises a shunt regulator configured to operate in acomparator mode.
 6. An overvoltage alarm conveying apparatus comprising:an overvoltage alarm circuit configured to generate an overvoltage alarmsignal based on a received overvoltage signal; a Zener diode; anisolating device configured to provide an isolated output signal; and acurrent limiting circuit configured to provide a current flow throughthe Zener diode to the isolating device when exposed to a voltageexceeding a rating of the Zener diode, wherein the Zener diode, theisolating device, and the current limiting circuit are configured tomaintain the overvoltage alarm signal generated by the overvoltage alarmcircuit if the overvoltage alarm circuit is unable to maintain theovervoltage alarm signal itself.
 7. The apparatus of claim 6, where theovervoltage alarm circuit comprises: a balancing circuit coupled to anenergy storage cell and configured to: monitor a voltage of the energystorage cell; and dissipate energy from the energy storage cell if thevoltage is at or above a first reference voltage; and an alarm circuitcoupled to the energy storage cell and configured to: generate an alarmwhen the voltage of the energy storage cell is at or above a secondreference voltage, and dissipate energy from the energy storage cellwhen the voltage is at or above the second reference voltage.
 8. Theapparatus of claim 1, further comprising a controller configured to:prevent dissipation of energy from the energy storage cell by thebalancing circuit and the alarm circuit when the voltage is below thefirst reference voltage, operate the balancing circuit to dissipate thefirst energy from the energy storage cell when the voltage is at orabove the first reference voltage, and operate the balancing circuit andthe alarm circuit to dissipate the first and second energies from theenergy storage cell when the voltage is at or above the second referencevoltage.
 9. The apparatus of claim 1, wherein each of the balancingcircuit and the alarm circuit comprises (1) a resistive voltage dividercomprising a first resistor and a second resistor and (2) a dissipativeleg comprising a passive dissipative component and an active dissipativecomponent, wherein each of the active dissipative components isconfigured to permit a discharging current to flow through therespective passive and active dissipative components based on a voltageoutput by the respective resistive voltage divider.